1. Field of the Invention
This invention relates in general to check valves for use in turbohydramatic transmission systems for automobiles and it deals more particularly with an improved type of third accumulator check valve used in such a system.
The invention is directed toward a third accumulator check valve so designed as to assure positive seating in operation, thus preventing damaging leakage which can result in unusual wear on an automobile transmission system.
With the advent of the modern automobile there came into being the need for and the immediate use of an automatic transmission system, whereby an automobile could be automatically shifted up into the series of gear ratios necessary to obtain the desired speed and shifted downwardly into the necessary gear ratios to decrease or stop that speed.
The oil operated hydramatic transmission was chosen as a very efficient means of achieving the foregoing ends and power is transmitted through oil to the gear drive train, providing additional torque multiplication when required by means of the sequential application of a series of gears to achieve the proper gear ratio and desired speed.
The drive train of an automobile comprises a series of intermeshing drive gears which must be continously engaged and disengaged automatically.
It has been found that the most desirable type of gears to be used are those which remain constantly intermeshed to avoid the clashing of gears which might be present if various gear combinations were suddenly engaged at different speeds.
It has been found that the most desirable medium for preventing the clashing of gears is to use a planetary gear set. The planetary gear set comprises a system of gears contained within an outer gear housing which has the contradictory name of "internal gear" because the teeth of this outer housing are contained on the periphery of the inside of the gear housing. Engaging the internal teeth of the internal gear are a series of pinion gears secured to a carrier. These pinion gears ride enmeshed with the gear teeth of the central gear located within the housing known as the "sun gear".
Through the rotation of various combinations of the foregoing described gears different gear ratios and speeds may be obtained with this type of system without the necessity of disengaging any gear teeth in the operation.
In the turbohydramatic drive, such as used in most General Motors automobiles, various combinations of planetary gear sets are employed, but an important feature of the operation of this system resides in the means of causing these gear sets to be engaged in the various combinations.
In the type of transmission with which we are dealing a torque converter smoothly couples through oil the engine power to the gear train and hydraulically provides additional torque multiplication when required. The engaging of the gears is entirely automatic and depends upon the automatic actuation of clutches to engage the gears.
A direct clutch is employed during one phase of the operation to engage a combination of the planetary gears. This clutch housing is engaged through an input drum to engage different combinations of gears during different modes of the clutch.
In one mode of the system, with which we are dealing in this patent application, an intermediate band is tightened against the outside of the direct clutch housing, preventing rotation of the same, and preventing the sun gear and input drum from rotating.
The intermediate band is released as the direct clutch is applied for third gear in order to allow the direct clutch to drive the sun gear.
In summary, it is necessary that there be a smooth and efficient operation of this system which is used to apply the third gear clutches and release the band that holds the transmission in second gear.
The intermediate band is applied and released by means of the use of an intermediate servo cylinder and piston system. This cylinder and piston is often referred to as the "intermediate servo".
In this servo system the outer end of the servo piston shaft is in communication with the intermediate band, and operates such that when the piston is in the mode with its shaft at maximum extension from the housing the shaft actuates the intermediate band to tighten this band on the clutch housing. When the servo piston shaft is withdrawn into its extreme position within the cylinder housing it loosens the intermediate band and applies the direct clutch by means of oil which is routed thereto to shift the drive train and transmission into a higher gear.
The intermediate servo is oil operated at all times through a remote system of shift valves, which valve the required oil into the proper path by reacting to the operation of a special governor for this system.
When direct clutch oil is routed to apply the direct clutch it also passes through an oil line connected through an accumulator check valve chamber to the release, or upper, side of the intermediate servo piston to release the band. In order to have a positive flow and smooth operation of the oil passing to the release side of the intermediate servo piston through the accumulator check valve chamber, the check valve must seat quickly, firmly and positively to prevent a hesitant operation of the system. This accumulator check valve is oftentimes referred to as the "third accumulator check valve" because it is used to shift from second to third gear in the operation of the vehicle.
As previously noted, oil passes through the accumulator check valve chamber into the servo cylinder against the upper or release side of the servo piston.
A commonly used type of accumulator check valve at the present time is a floating, partially gravity actuated, cylindrical valve. The valve has a conical configuration of its upper end adapted to seat in an exhaust orifice when the valve is actuated to allow a constant flow of oil at constant pressure around the check valve into the servo cylinder. The present valve has an annular shoulder disposed opposite an inlet port for the valve chamber, through which incoming oil operates against the lower side of the shoulder to lift the valve and hold the same in the seated position. It will be remembered that it is important for the exhaust orifice to be completely sealed in order to provide constant pressure on the top side of the servo piston.
In the past the presently provided floating check valves of this design have not achieved the desired results. The means of positive seating depends upon the pressure of oil against the lower surface of the shoulder and bottom of the valve to maintain the same in the seated position. Because of its design it seats much too slowly (or not at all) to stop the exhaust of fluid pressure that is used to apply the third gear clutches and release the intermediate band that holds the transmission in second gear. This slow seating causes a slow or hesitant shift, creating excessive wear on the band and high clutches.
At low speeds in high gear the flow of fluid past the shoulder of the valve is not adequate to keep the valve seated, causing the valve to exhaust fluid pressure through the exhaust orifice and allow the band to partially apply (or drag) due to the release of pressure on the top side of the servo piston, and allow the high clutches to slip. This drag and slip causes premature band and clutch failure. It also generates excessive heat that burns the transmission fluid and friction material.
The floating check valve system is very desirable due to the fact that there are not a number of combined moving parts to this type of valve which can cause friction or wear out over the operation of a transmission system. The floating valve has advantages over the lever system or spring type operated plug valves because there are fewer parts to wear and become inoperative and because the design is simple and economical to manufacture.
The most widely used of the presently designed floating check valves in this application is the cylindrical valve before mentioned, having a conical top which seats in the exhaust orifice and provided midway of its length with a projecting annular shoulder and a projecting annular base located at its lower end. This is a solid cylindrical shape object without any inner bore. The reason these valve designs do not work properly and seat efficiently lies in the fact that the outside diameter of the shoulder of the floating valve piece is approximately 0.450 inches in diameter with the piece running in a 0.5000 inches bore. This valve depends upon the flow of fluid around the valve to lift it into the seated position and to hold it there. The axial length of the valve is such that when the valve is released it falls down the bore until the shoulder is even with the input oil feed hole and not above it as should be the case. This makes it very difficult for the flow of the oil to pick up the valve around the shoulder and lift it into the seated position, thereby causing delay in seating.
Therefore, it is very desirable that a different shape be designed for the floating valve body and that the location of any shoulder on the body be such that the body of the valve may be easily lifted by means of the pressure of the oil flow into the seated position. It is also desirable that some auxiliary means be found to allow more free flow of fluid to apply to a greater surface of the valve body in some manner to lift the valve quickly into the seated position and assist in holding it there.
2. Consideration of Prior Art
After competent search, no existing devices of the type disclosed in the present invention were found, there being seven references which were considered, but which do not appear to conflict with the present invention or anticipate the apparatus or the objects and purposes for which it was designed.
The prior art discloses the following U.S. Pat. Nos.:
______________________________________ W. G. Buchner, et al Check Valve 2,928,417 G. N. Chatham, et al Check Valve 3,027,913 J. J. Searles Control Valve 3,344,681 K. A. Bailey Flow Control 3,682,043 Jerry R. Marlowe Systems K. A. Bailey Flow Control 3,757,644 Jerry R. Marlowe System K. A. Bailey Transmission 3,789,963 Jerry R. Marlowe Control Bruce A. McElhoe Irrigation 4,031,915 G. Tabrah System ______________________________________
The patent to Buchner discloses a check valve reciprocating within a counterbore 32. This structure is not the same as that in the present invention and the orifice is part of a larger bore with the valve seated in a reverse position in this bore to occlude the passage of fluid through a hollow chamber within the valve. Fluid pressure to the right unseats the valve and allows fluid to pass through the hollow chamber in the valve and out the port. The entire valve body itself moves to expose the radial ports 56. This is not the same principle as the present invention.
The patent to Chatham shows a plug 61 within a bore 69 spring biased by means of the spring 72 into a seated position in the bore of the inlet port 68. An outlet port 70 is provided and the plug 61 must be moved a considerable distance from the seat of the port 68 in order for fluid to bypass and exit through the port 70. The bore 63 on the inside of the plug 61 is provided in conjunction with the groove 64 to allow fluid from the backside of the valve to escape through the port 66 into the groove 64 and out through the outlet port 70. FIGS. 2 and 3 are simply modifications of this structure and the structure does not in any way resemble the structure of the present invention nor does it operate in the same manner.
The patent to Searles shows a control valve system for an automatic power transmission. However, the servo systems are spring piston operated by fluid but do not show an accumulator valve similar to the one in the present invention. This invention deals primarily with the entire system and is not directed to a special type of accumulator check valve as we have in the present invention. It does not disclose a valve of similar nature.
The Bailey et al U.S. Pat. No. 3,682,043 shows a slow control system for an automatic transmission. However this is directed to a system as a whole for the pumping and flowage of oil in the transmission system but does not deal with an accumulator check valve of the type shown in the present invention.
The Bailey et al U.S. Pat. No. 3,757,644 shows a flow controlled control system for motors which again deals with an overall system and is not directed to a check valve for a third accumulator as is the present invention. This does not deal with the same type of principle involved or suggest the same.
The Bailey et al U.S. Pat. No. 3,789,963 shows another transmission control system directed to the overall pumping and valving system for an entire transmission which does not direct its attention to a check valve for the third accumulator valve in a transmission such as we have done in the present invention. There is no similarity or suggestion of the present invention by this patent.
The patent to McElhoe, et al, is directed to an irrigation system flushing valve. This patent is directed to an entirely different type of system and does not involve a check ball or an accumulator valve. The valve body in this system is hollow and the valve itself requires a withdrawal to a position such as shown in FIG. 5 in order for there to be an unrestricted flow against the valve through the outlet ports 52 and 53. This patent does not embody the same principle as the accumulator check valve in the present invention and does not disclose nor suggest the present invention.